Typical rubber hoses, for example, made of a blend of acrylonitrile-butadiene rubber and polyvinyl chloride (NBR/PVC blend) or fluoro rubber (FKM) which is excellent in resistance to gasoline permeability, have been used for conveying fuel (fuel such as gasoline for engine) for automobiles or the like in view of their high vibration-absorbability, easy assembling or the like. However, for the purpose of global environment protection, the regulations have been recently tighten against permeation of fuel for automobiles or the like, and are anticipated to be further tighten in the future.
Therefore, such hoses for conveying fuel or the like are required further permeation resistance.
And, hoses for conveying fluid such as hydrogen gas used in fuel cells, or for conveying carbon dioxide gas refrigerant are required extremely high permeation resistance to such conveyed fluid as hydrogen gas, carbon dioxide gas.
However, with regard to this requirement hoses configured by organic materials only such as rubber or resin are difficult to satisfy such required resistance.
Under the circumstances, it is considered to form a composite hose by combining with a corrugated metal tube as a barrier layer against permeation of conveyed fluid.
For example, U.S. Pat. No. 6,354,332 and JP, A, 2001-182872 disclose a composite hose with a corrugated metal tube of this type. Here, a corrugated metal tube and an elastic layer such as rubber layer are combined, and a reinforcing layer is provided on the elastic layer to construct a composite hose which has permeation resistance and pressure resistance as well as vibration damping property and mountability or assemblability. The reinforcing layer is usually constructed by winding or braiding a reinforcing wire or reinforcing thread around an outer periphery of the elastic layer or by overlaying a layer braided with a reinforcing wire or reinforcing thread around the outer periphery of the elastic layer. In many cases, a layer having elasticity such as a rubber layer is formed on an outer side of thus constructed reinforcing layer.
By the way, in case where an elastic layer, for example, made of rubber, is provided on an outer periphery of the corrugated metal tube, a rubber material is, for example, extruded or overlaid therearound. Here, the rubber material is required to have a proper thickness in order to secure a stable and axially continuous processability. Therefore, as the elastic layer of a certain thickness is interposed between the corrugated metal tube and the reinforcing layer even on positions of the corrugation hills of the corrugated metal tube, as a result, a certain distance is defined between the corrugation hills and the reinforcing layer. Also, when processing continuously in an axial direction, sometimes uneven thickness is caused in the elastic layer or uneven tension is caused in the reinforcing layer, and thereby the reinforcing layer has a slight slackness or looseness in a radial direction with respect to the corrugated metal tube. That is, in many cases, the reinforcing layer does not act a restraining force on the corrugated metal tube, for example, to restrain expansion of the corrugated metal tube once a high pressure is exerted to the corrugated metal tube by an internal fluid or at the same time when high pressure is exerted thereto by the internal fluid. So, for example, in such service environment or use environment that the corrugated metal tube is repeatedly subject to a stress beyond a fatigue-limit of the corrugated metal tube, if thus constructed composite hose with a corrugated metal tube is used, the corrugated metal tube is possibly fatigue broken. That is, thus composite hose with a corrugated metal tube cannot secure a reliable pressure resistance to the internal fluid. Inconvenience such as insufficient pressure-resistance in the composite hose with a corrugated metal tube is also caused in case where a rubber material is not filled in corrugation valleys of the corrugated metal tube and thereby gaps are defined between the corrugation valleys and the reinforcing layer.
As for technique to enhance durability of a corrugated metal tube, the techniques as disclosed in JP, A, 57-86688 (1982-86688) and JP, A, 11-159616 (1999-159616) are known. JP, A, 57-86688 disclosed that a metal bellows is exerted by an internal pressure, and it is stretched to extend a corrugation pitch in an axial direction, and the durability is enhanced by work hardening in this process. However, this necessarily results in different axial length, for example, largely different axial length among the corrugated metal tubes. On the other hand, JP, A, 11-159616 discloses that a sectional shape of a corrugated portion of a corrugated metal tube is changed from a U-shape to a S-shape, and this specific shape effectively enhances the durability. It is difficult to immediately employ both of the techniques.
The present invention is made under the foregoing circumstances. It is an object of the present invention to provide a composite hose with a corrugated metal tube which has an excellent pressure resistance to an internal fluid as well as vibration damping property and mountability, and consequently may increase service life of the composite hose, and to provide a method for making thus constructed composite hose with a corrugated metal tube. And it is an object of one aspect of the present invention to provide the composite hose with a corrugated metal tube wherein durability is improved both against repeated internal pressures and repeated bending deformations.